Perpendicular magnetic recording (PMR) has been developed in part to achieve higher recording density than is realized with longitudinal magnetic recording (LMR) devices and is believed to be the successor of LMR for next generation magnetic data storage products and beyond. A single pole writer combined with a double layered recording media has the intrinsic advantage of delivering higher write field than LMR heads and enables a continuous increase in recording density required for advances in hard disk drive (HDD) technology. A conventional PMR write head as depicted in FIG. 1 typically has a main (write) pole 10 with a small surface area (pole tip) at an air bearing surface (ABS) 5 and a flux return pole (opposing pole) 8 which is magnetically coupled to the write pole through a trailing shield 7 and has a large surface area at the ABS. Magnetic flux in the write pole layer 10 is generated by coils 6 and passes through the pole tip into a magnetic recording media 4 and then back to the write head by entering the flux return pole 8. The write pole concentrates magnetic flux so that the magnetic field at the write pole tip at the ABS is high enough to switch magnetizations in the recording media 4.
To achieve high areal recording density with PMR technology, a key requirement for the PMR writer design is to provide large field magnitude and high field gradient in both down-track and cross-track directions. In practice, these two requirements are often traded off with each other to balance the overall performance. To improve the down-track field gradient, a trailing shield PMR writer design has been widely applied today. In FIG. 2, a view from the ABS plane is shown of a conventional trailing shield PMR writer in which a magnetic write shield 12 is placed above the top edge 10b of the write pole 10 by a certain distance d. The bottom or leading edge 10a of the write pole 10 is so designated because it is at the front of the write pole as it moves in the y or down-track direction. With this design, the down-track gradient is improved at the expense of reducing write field. In the cross-track or x direction, however, there is still a quite large detrimental fringe field (not shown) leading out from the write pole 10.
Referring to FIG. 3a, another prior art design is illustrated that was proposed by M. Mallary and described in “One Terabit per Square Inch Perpendicular Recording Conceptual Design”, IEEE, Trans. Magn., Vol. 38, July, 2002. To further improve cross-track field gradient, a full side shield writer structure is used to limit the excessive fringe field onto the adjacent track. For example, the writer in FIG. 2 may be modified by adding one side shield 13 along one side of the write pole 10 and a second side shield 14 along the opposite side of the write pole. The side shields 13, 14 have a thickness t equal to the thickness of the write pole 10. Note that the side shields may have sloped sides that parallel the slope in the write pole sides and maintain a spacing or side gap s therebetween as viewed from the ABS. Depending on the size of side gap s, field magnitude could drop below the minimal performance requirement. FIG. 3b shows a down-track view of the PMR writer in FIG. 3a. The main pole layer 10 has a write pole 10p at the ABS 5-5, a main pole section 10m, and a flared section 10f that connects the write pole 10p and main pole section 10m. 
Referring to FIG. 4, a finite element method (FEM) model shows a narrower head field width, sharper cross-track field gradient, and significantly smaller skirt field in the head profile 18 of a side shielded pole compared to the profile 17 of a trailing shielded pole. Based on this data, one can expect a very narrow track write width and much less adjacent track erasure in a side shielded head. However, most of the actual heads that feature side shields exhibit much poorer adjacent track erasure even though FEM models indicate less skirt in the head field profile. In addition, track erasure is not limited to adjacent tracks but can occur in tracks located several track widths away from the writing area. This phenomenon has been observed in many PMR writers with a side shielded configuration and appears to be a fatal flaw in a magnetic recording system.
Unfortunately, none of the prior art structures provide satisfactory control of field magnitude and field gradient in both the down-track and cross-track directions. Therefore, an improved write structure is necessary to achieve the high performance required for advanced devices with narrow track widths and high recording density. A routine search of the prior art revealed the following references. U.S. Pat. Nos. 4,656,546 and 4,935,832 discuss side shields to control fringing flux.
U.S. Pat. No. 6,954,340 describes a side shield PMR write structure wherein the distance between the ABS of the main pole and the bottom layer of a double layer recording medium is not more than two times shorter than the write gap distance between the main pole and a side shield.
U.S. Pat. No. 6,995,950 discloses reducing the flux gathering capacity of shields by reducing shield height but there are no specifics as to the height of the shield.
U.S. Patent Application No. 2005/0068678 shows side shields connected to a return pole piece on one side and to a trailing shield on an opposite side.
U.S. Patent Application No. 2006/0082924 describes a wrap-around shield where the height of the shield at the main pole side is greater than the height of the shield at the return pole.
U.S. Patent Application Nos. 2006/0000794 and 2006/0044682 disclose a trailing shield gap thickness which is different than a side shield gap thickness.
In U.S. Patent Application No. 2005/0141137, a trailing side shield has a thickness (Gd) equal to or less than the throat height near the main pole but Gd may be larger than the throat height in a portion of the shield that is a farther distance from the main pole to prevent the trailing shield from defoliating along the ABS.
U.S. Patent Application No. 2007/0146929 describes a main pole with a first flare adjacent to an air bearing surface and a second flare adjacent to the first flare but a greater distance from the ABS. There is a non-magnetic film between the first flare and a first magnetic layer along the ABS. The first magnetic layer provides shielding to prevent flux leakage to adjacent tracks. However, controlling the first flare thickness and second flare thickness could be a manufacturing issue.